1,4-Butanediol (hereinafter, sometimes simply referred to as “1,4BG”) is a raw material of tetrahydrofuran (hereinafter, sometimes simply referred to as “THF”) used as a solvent and is a substance useful also as a raw material of a polyester material such as polybutylene terephthalate (hereinafter, sometimes simply referred to as “PBT”).
Conventionally, a method for industrially producing 1,4BG is known. For example, there are known a method for producing 1,4BG by hydrogenation and hydrolysis of 1,4-diacetoxy-2-butene that is obtained by diacetoxylation of butadiene, a method for obtaining a 1,4BG-containing crude hydrogenation product by using maleic anhydride as a raw material and hydrogenating it, a method for producing 1,4BG by hydrogenating butynediol that is obtained by using acetylene as a raw material and contacting it with an aqueous formaldehyde solution, a method for obtaining 1,4BG through oxidation of propylene, a method of hydrogenating succinic acid obtained by a fermentation process, and a method for direct production from sugar by a fermentation process.
The thus-obtained crude 1,4BG sometimes contains 2-(4-hydroxybutoxy)-tetrahydrofuran as an impurity, and removal of this substance by distillation is difficult, because its boiling point is close to that of 1,4BG. Patent Document 1 describes a method of decomposing 2-(4-hydroxybutoxy)-tetrahydrofuran in the crude 1,4BG by using various platinum element-supported catalysts so as to reduce the substance. Patent Document 2 reveals the fact that in a continuous process for producing 1,4BG by hydrogenation and hydrolysis of 1,4-diacetoxy-2-butene obtained by diacetoxylation of butadiene, a hydrogenation catalyst powder inflows in the distillation step to cause production of 2-(4-hydroxybutoxy)-tetrahydrofuran in 1,4BG in a distillation column and when PBT is produced using thus obtained 1,4BG, PBT is colored. Patent Document 3 describes a method where the temperature and pressure inside an esterification reaction tank and a distillation column for producing PBT are appropriately controlled to decompose 2-(4-hydroxybutoxy)-tetrahydrofuran under acidic conditions so as to achieve conversion to 2,3-dihydrofuran, 2-hydroxytetrahydrofuran and the like and these substances are removed together with water, THF and the like by the distillation column from the esterification reaction tank.